The best definition of the process of gastrulation is that it is a process where

Options

A. (a) blastocoel is formed
B. (b) zygote gets converted to larva
C. (c) cells move the occupy their definite position
D. (d) simple layered blastula becomes two layered

Answer

**Step-by-Step Solution:**

1. **Understanding Gastrulation**: Gastrulation is a crucial post-fertilization event that occurs after the formation of the zygote. It is the process where the single-layered blastula transforms into a multi-layered structure known as the gastrula.

2. **Formation of Blastula**: After fertilization, the zygote undergoes cleavage, leading to the formation of an 8-cell stage, which further develops into a blastula through a process called blastulation. The blastula contains a fluid-filled cavity known as the blastocele.

3. **Transformation to Gastrula**: During gastrulation, the blastula undergoes significant cellular rearrangement, resulting in the formation of the gastrula. This process involves morphogenetic movements where cells move to specific positions.

4. **Types of Gastrula**: The gastrula can be classified into two types:
- **Early Gastrula**: This is a two-layered structure comprising the ectoderm and endoderm.
- **Late Gastrula**: This is a three-layered structure that includes the addition of a mesoderm layer between the ectoderm and endoderm.

5. **Significance of Gastrulation**: The primary significance of gastrulation is to establish the basic body plan of the organism by arranging the three germ layers (ectoderm, mesoderm, and endoderm) in a specific order. These layers are responsible for forming various organs and tissues in the developing organism.

6. **Evaluating Options**:
- **Option A**: Incorrect, as blastocele formation occurs during blastulation, not gastrulation.
- **Option B**: Incorrect, as the zygote does not convert to a larva in human development.
- **Option C**: Correct, as it accurately describes the movement of cells to occupy their definite positions during gastrulation.
- **Option D**: Incomplete, as it does not fully capture the process of gastrulation.

7. **Conclusion**: The best definition of the process of gastrulation is that it is a process where cells move to occupy their definite positions, leading to the formation of the three germ layers.

**Final Answer**: C - Cells move to occupy their definite position.

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